Radio-Frequency Tuner with Differential Converter

ABSTRACT

A system for tuning a radio-frequency signal includes a first input path, a second input path, a common reference generator, a selector, a mixer, and a filter. The first input path and the second input path propagate a first single-ended input signal and a second single-ended input signal, respectively, to the selector. The selector converts the first single-ended input signal and the second single-ended input signal into a first differential input signal and a second differential input signal, respectively, using a reference signal generated by the common reference generator. 
     The selector selectively couples one of the first and the second input path to an input of the mixer. The mixer downconverts a selected on of the differential input signals received from the selector. The filter attenuates a portion of the downconverted input signal outside a passband associated with the filter.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to radio-frequency signal tuners and,more particularly, to a multi-band digital broadcast tuner.

BACKGROUND OF THE INVENTION

Recent developments in communication technology have led to theintroduction of mobile digital communication devices that provideseveral different types of service. As a result, modern communicationdevices may be faced with the task of receiving and processing a varietyof different types of signals. This flexibility may provide significantdesign challenges when combined with the space and power restrictionsassociated with mobile devices.

In particular, receivers that can tune across multiple sub-bands of theradio-frequency spectrum, including sub-bands of different sizes, can bedifficult to design. Designing a receiver to accept signals withinmultiple sub-bands of varying sizes may compromise the receiver'sperformance when receiving signals in some or all of the sub-bands. Bothlinearity and noise characteristics may be sacrificed to providefrequency flexibility. Furthermore, the power limitations faced bymobile devices result in headroom requirements for such devices thatcreate additional design challenges.

SUMMARY OF THE INVENTION

In accordance with the present invention, the disadvantages and problemsassociated with signal tuners have been substantially reduced oreliminated. In particular, a multi-band broadcast tuner is provided.

In accordance with one embodiment of the present invention, a system fortuning a radio-frequency signal includes a first input path, a secondinput path, a common reference generator, a selector, a mixer, and afilter. The first input path and the second input path propagate a firstsingle-ended input signal and a second single-ended input signal,respectively, to the selector. The selector converts the firstsingle-ended input signal and the second single-ended input signal intoa first differential input signal and a second differential inputsignal, respectively, using a reference signal generated by the commonreference generator.

The selector selectively couples one of the first and the second inputpath to an input of the mixer. The mixer downconverts a selected on ofthe differential input signals received from the selector. The filterattenuates a portion of the downconverted input signal outside apassband associated with the filter.

In accordance with another embodiment of the present invention, a systemfor receiving radio-frequency signals includes a conductive path, anoscillator, a tuning path, and a mixer. The conductive path is capableof coupling an input signal to a signal input of the mixer. The inputsignal is associated with one or more frequencies within a first rangeof frequencies. The oscillator is capable of generating an oscillatorsignal that is associated with a frequency within a second range offrequencies. The tuning path is capable of coupling the oscillatorsignal to a tuning input of the mixer and the tuning path crosses theconductive path at least at a first point.

Additionally, the frequency divider is located on the tuning pathbetween the first point and the tuning input of the mixer and is capableof generating a divided oscillator signal based on the oscillatorsignal. The divided oscillator signal is associated with a frequencywithin the first range of frequencies. Furthermore, the mixer is capableof receiving, at the signal input of the mixer, the input signal fromthe conductive path and receiving, at the tuning input of the mixer, thedivided oscillator signal from the tuning path. The mixer is alsocapable of downconverting the input signal based on the dividedoscillator signal and outputting at least a portion of the downconvertedinput signal.

Important technical advantages of certain embodiments of the presentinvention include power saving benefits, space-saving packaging, andgreater operational flexibility. In particular, certain embodiments maybe capable of operating with reduced headroom. Additionally, certainembodiments may be able to isolate internal signals from one another inan improved manner so as to provide greater noise-reduction. Othertechnical advantages of the present invention will be readily apparentto one skilled in the art from the following figures, descriptions, andclaims. Moreover, while specific advantages have been enumerated above,various embodiments may include all, some, or none of the enumeratedadvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a multi-band tuner according to a particularembodiment of the present invention;

FIGS. 2A and 2B are detailed illustrations of portions of a basebandstage that may be included in particular embodiments of the multi-bandtuner; and

FIG. 3 is a detailed illustration of a frequency generation circuit thatmay be utilized in a particular embodiment of the multi-band tuner.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram illustrating functional components of aparticular embodiment of a tuner 10 capable of tuning radio-frequencysignals received over multiple sub-bands of the radio-frequencyspectrum. As shown in FIG. 1, tuner 10 includes a radio-frequency (RF)stage 20, a mixing stage 30, a baseband stage 40, a programmableinterface 50, and a frequency generation circuit 60. Additionally, tuner10 couples to a plurality of antennas 12 through which tuner 10 receivesinput signals 90. Tuner 10 isolates and outputs information within aparticular range of frequencies, or “channel”, selected by a user oranother component coupled to tuner 10. In particular embodiments, tuner10 is capable of tuning input signals 90 received within differentsub-bands of varying size without substantial deterioration inperformance. Additionally, in particular embodiments, based on theconfiguration of the various elements of tuner 10, tuner 10 may becapable of operating with low headroom and of limiting interferencebetween internal signals used by the stages of tuner 10 as described ingreater detail below.

Antennas 12 receive radio-frequency signals from terrestrial and/orsatellite sources and transmit these signals to inputs ports 22 of tuner10. Antennas 12 may represent and/or include any appropriate componentsto receive radio-frequency signals. In particular embodiments, tuner 10is configured to receive signals in multiple bands of theradio-frequency spectrum, and tuner 10 may couple to a separate antenna12 for each frequency band tuner 10 is capable of receiving. Althoughthe description below focuses on embodiments in which tuner 10 receivesinput signals 90 through antennas 12, particular embodiments of systemmay omit antennas 12. In such embodiments, tuner 10 may receive inputsignals 90 from other components coupled to tuner 10 such as elements ofan external cable transmission system.

In the illustrated embodiment, tuner 10 couples to an ultra highfrequency (UHF) antenna 12 a through which tuner 10 receives signalshaving a frequency within an appropriate portion of the UHF spectrum, avery high frequency (VHF) antenna 12 b through which tuner 10 receivessignals having a frequency within an appropriate portion of the VHFspectrum, and an L-band antenna 12 c through which tuner 10 receivessignals having a frequency within an appropriate portion of the L-Band.For example, particular embodiments of tuner 10 may be configured toreceive signals within the 470 MHz to 2 GHz sub-band of the UHF spectrumfrom UHF antenna 12 a, to receive signals within the 150 MHz to 260 MHzsub-band of the VHF spectrum form a VHF antenna 12 b, and to receivesignals within the 1.5 to 1.6 GHz sub-band of the L-Band spectrum froman L-Band antenna 12 c. As a result, in particular embodiments, tuner 10may be operable to receive signals within a wide sub-band fromparticular antennas 12 and within a narrow sub-band from the same orother antennas 12. Moreover, as described in greater detail below, tuner10 may be capable of tuning across both the wide sub-bands and narrowsub-bands using a common mixer and/or other shared components.

RF stage 20 receives input signals 90 from input ports 22 and conditionsinput signals 90 to facilitate tuning of input signals 90 by basebandstage 40. RF stage 20 conditions input signals 90 in any appropriatemanner based on the characteristics of the input signals 90 received bytuner 10 and the configuration of mixers 32 and/or other components ofbaseband stage 40. In the illustrated embodiment, RF stage 20 includes aplurality of input paths 100 connecting each of tuner input ports 22 toa signal converter 24. Nonetheless, RF stage 20 may include anyappropriate number and configuration of components to perform therelevant signal-conditioning based on the input signals 90 received bytuner 10 and the characteristics and capabilities of the othercomponents of tuner 10.

In the illustrated embodiment, RF stage 20 includes a plurality of inputpaths 100 connecting each of tuner input ports 22 to signal converter24. Signal converter 24 couples one of input paths 100 to mixing stage30 based on a frequency or channel selected by the user and/or otherappropriate factors. Additionally, signal converter 24 may convert theinput signals 90 received by RF stage 20 in an appropriate manner tofacilitate the input of these signals to mixing stage 30. In particularembodiments, signal converter 24 may perform single-ended todifferential conversion, voltage-mode to current-mode conversion, and/orany other suitable form of processing, conditioning, and/or conversionappropriate based on the configuration of tuner 10. Moreover, signalconverter 24 may induce gain in the selected signal providing additionalcontrol over the signal strength and distortion characteristics ofpreprocessed signal 92.

To provide such signal conditioning, tuner 10 may include one or moreinput paths 100 containing various combinations of components capable ofimplementing the relevant conditioning. For example, as shown, firstinput path 100 a includes a first attenuator 102, a first tunablebandpass filter 104, a low noise amplifier 106, a second tunablebandpass filter 108, and a second attenuator 102 that are connected inseries and that couple tuner input port 22 a to signal converter 24.Second input path 100 b includes a third tunable bandpass filter 112, alow noise filter 106, a fourth tunable bandpass filter 114, and anattenuator 102 that are connected in series and that also couple tunerinput port 22 a to signal converter 24. Third input path 100 c includeslow noise amplifier 106 and couples tuner input port 22 b to signalconverter 24. Fourth input path 100 d includes a low noise amplifier 106that couples tuner input port 22 c to signal converter 24.

The presence of attenuators 102 and bandpass filters 104 and 108 ininput paths 100 a and 100 b may facilitate reception of input signals 90across a wide sub-band through input paths 100 a and 100 b. As a result,in particular embodiments, RF stage 20 may include one or more inputpaths 100 (such as input paths 100 a and 100 b) configured for use withantennas 12 receiving signals across a wide sub-band and also one ormore input paths 100 (such as input paths 100 c and 100 d) configuredfor use with antennas 12 receiving signals across a narrow sub-band.Moreover, because of the various configurations of input paths 100,tuner 10, in particular embodiments, may be capable of receiving andtuning broadband and/or narrowband input signals 90 that are transmittedover a very wide sub-band of the RF spectrum and also be capable ofreceiving and tuning broadband and/or narrowband input signals 90 thatare received over a very narrow sub-band of the RF spectrum withoutsubstantial deterioration in performance. For example, in particularembodiments, tuner 10 may be capable of receiving and tuning signalstransmitted over an approximately 1.5 GHz sub-band (from 470 MHz to 2GHz) of the UHF band of the RF spectrum as well as receiving and tuningsignals transmitted over an approximately 100 MHz sub-band (150 MHz to260 MHz) of the VHF band of the RF spectrum without substantialdeterioration of performance when tuning within either sub-band.Although these values are provided for purposes of illustration, tuner10 may, in particular embodiments, be configured to allow tuning acrossany appropriately sized sub-bands of any portions of the RF spectrum.

Each of input paths 100 is operable to connect a particular tuner inputport 22 to signal converter 24. Moreover, in particular embodiments,multiple input paths 100 may connect a particular tuner input port 22 tosignal converter 24. In such embodiments, the multiple input paths 100may each provide different forms of processing to the input signals 90received by that tuner input port 22. For example, in the illustratedembodiment, both input paths 100 a and 100 b connect tuner input port 22a to signal converter 24. Based, in part, on the presence of theadditional attenuator 102 in first input path 100 a, first input path100 a, however, may be more tolerant of interference, while second inputpath 100 b may allow for more robust frequency reception. Depending onstrength of signal and/or other operational considerations, the user ortuner 10 itself may select an appropriate one of input path 100 a andinput path 100 b to provide UHF signals to mixing stage 30. Furthermore,as described further below, gain and attenuation elements may bedistributed throughout particular input paths 100 to allow tuner 10 tobe configured for an optimal tradeoff between distortion and noise.

Signal converter 24 couples one of input paths 100 to mixing stage 30based on a frequency or channel selected by the user and/or otherappropriate factors. Thus, a user or other device controlling tuner 10can select a particular input signal 90 and/or a particular form ofprocessing to perform on the relevant input signal 90 by controlling theoperation of signal converter 24.

Additionally, signal converter 24 may convert the input signals 90received by RF stage 20 in an appropriate manner to facilitate the inputof these signals to mixing stage 30. Signal converter 24 then outputsthe selected input signal 90 as one or more preprocessed signals 92. Inparticular embodiments, signal converter 24 converts single-ended,voltage-mode input signals 90 received by tuner 10 into a differentialpair of current-mode preprocessed signals (92 a and 92 b). Moreover,signal converter 24 may induce gain in the selected signal providingadditional control over the signal strength and distortioncharacteristics of preprocessed signals 92.

Furthermore, in particular embodiments, tuner 10 may be housed in asingle integrated circuit and signal converter 24 may be coupled to asingle reference voltage 192 provided by components internal and/orexternal to tuner 10 for multiple bands. Reference voltage 192 may beprovided by any appropriate component or collection of components. Inparticular embodiments, reference voltage 192 is provided by a chargedcapacitor. In general however, reference voltage 192 may be provided byany other component or components capable of providing a voltage havingthe desired electrical characteristics. By utilizing reference voltage192 produced by the same component or components to effectuate thesingle-ended-to-differential conversion of multiple input signals 90,tuner 10 may reduce the number of external components necessary tooperate tuner 10 and/or the amount of silicon space required for theinternal components of tuner 10. This may result in both size and costsavings.

Returning to the components of tuner 10, mixing stage 30 downconvertspreprocessed signal 92 based on the selected tuning frequency andoutputs a downconverted signal 94. In the illustrated embodiment, mixingstage 30 includes a pair of mixers 32 a and 32 b. More specifically,mixer 30 includes an in-phase mixer 32 a and a quadrature mixer 32 b.Mixing stage 30 may, however include any appropriate number andconfiguration of components to downconvert a selected portion of thereceived preprocessed signal 92. The contents of a particular embodimentof mixing stage 30 are described in greater detail below with respect toFIGS. 2A and 2B.

Baseband stage 40 receives downconverted signal 94 from mixing stage 30,isolates the baseband portion of downconverted signal 94, and generatesone or more output signals 96 that include the baseband portion ofdownconverted signal 94. Tuner 10 then outputs, at one or more outputpins 38, an output signal 96 that contains the baseband portion of thedownconverted signal. In particular embodiments, output pins 38 maycouple to a demodulator or other appropriate component for subsequentprocessing and/or use of output signals 96. In the illustratedembodiment, baseband stage 40 includes a pair of baseband filters 42.Although the filters included in baseband stage 40 are described as“baseband” filters, particular embodiments of tuner 10 may include anysuitable type of filters appropriate based on the configuration of tuner10. Moreover, although baseband stage 40, as illustrated, includesparticular components, baseband stage 40 may include any appropriatenumber and configuration of components to downconvert a selected portionof the received preprocessed signal 92 and/or isolate the basebandportion of the downconverted signal 94.

Frequency generation circuit 60 generates one or more periodic signalsfor use by mixing stage 30 to downconvert preprocessed signals 92received by mixing stage 30. In particular embodiments, frequencygeneration circuit 60 may include one or more frequency dividers locatednear mixing stage 30 to adjust the frequency of the generated periodicsignal to a frequency useable by mixing stage 30. The placement of suchfrequency dividers may provide additional advantages for particularembodiments of tuner 10 as described in greater detail below withrespect to FIG. 3.

In operation, RF stage 20 receives input signals 90 at input ports 22.RF stage 20 may receive input signals 90 from any appropriate sources.In particular embodiments, RF stage 20 may couple to a plurality ofantennas (not shown) through input ports 22, and input signals 90 mayrepresent signals received by these antennas and transmitted to inputports 22. After being received at input ports 22, input signals 90propagate over input paths 100 to signal converter 24.

Based on the input received from programmable interface 50, signalconverter 24 selects a particular input path 100 to output. Depending onthe configuration of tuner 10, signal converter 24 may, by selecting aparticular input path 100 to output, select the source from which tuner10 receives the input signal. For example, in the illustratedembodiment, signal converter 24 may, by selecting between input paths100 b-d, select between input signals 90 received at input ports 22 a-crespectively. Additionally, in particular embodiments, multiple inputpaths 100 may couple a particular input port 22 to signal converter 24.In such embodiments, signal converter 24 may also, by selecting aparticular input path 100, select the conditioning to be performed tothe selected input signal 90. For example, in the illustratedembodiment, both input paths 100 a and 100 b couple input port 22 a tosignal converter 24 but, as a result of the different componentsincluded in input paths 100 a and 100 b, the two input paths 100condition input signals 90 received at input port 22 a in differentmanners. As a result, tuner 10 may be reconfigured dynamically to adjustto changes in operating conditions or performance requirements.

In particular embodiments, signal converter 24 may also convert theselected input signal 90 from a single-ended signal to a differentialsignal pair and/or from a voltage-mode signal to a current-mode signal.Because low noise amplifiers 106 in the various input paths 100 amplifyinput signals 90 before they are converted, RF stage 20 may provideseveral advantages. For example, by amplifying input signals 90 prior tovoltage-to-current conversion, particular embodiments of RF stage 20 maylimit the current consumption by tuner 10. Moreover, by amplifying inputsignals 90, prior to converting them from single-ended signals todifferential signal pairs, particular embodiments of RF stage 20 mayproduce improved noise figures. Additionally, by converting inputsignals 90 to differential signals before transmitting input signals 90to mixer 30, tuner 10 may achieve better even-order distortionperformance.

After any appropriate conversion and amplification, signal converter 22outputs the selected input signal 90 to baseband stage 40 aspreprocessed signal 92. In particular embodiments, signal converteroutputs two copies of preprocessed signals 92. In the illustratedembodiment, each copy of preprocessed signal 92 represents acurrent-mode, differential signal pair (92 a and 92 b).

Mixers 32 a and 32 b of baseband stage 40 each receive a copy ofpreprocessed signal 92. As described in greater detail below withrespect to FIG. 3, frequency generation circuit 60 provides mixers 32 aand 32 b with a tuning signal 86 and a phase-shifted version of tuningsignal 86, referred to as phase-shifted tuning signal 88, both having afrequency equal to the selected tuning frequency. Based on tuning signal86 and phase-shifted tuning signal 88, respectively, mixers 32 a and 32b downconvert a particular frequency component or channel withinpreprocessed signal 92 so that the relevant frequency or channelpossesses a lower center frequency. More specifically, mixers 32 a and32 b downconvert the relevant frequency component or channel so that therelevant frequency component or channel is centered at the desiredbaseband frequency. In particular embodiments, this frequency may besubstantially near 1 Hz. After downconversion, preprocessed signals 92are output by mixers 32 a and 32 b as downconverted signals 94. Morespecifically, in the illustrated embodiment, mixers 32 a and 32 b outputdownconverted signal 94 as an in-phase downconverted signal pair 94 aand 94 b and a quadrature downconverted signal pair 94 c and 94 d.

Baseband stage 40 receives downconverted signals 94 output by mixingstage 30. Baseband filters 42 in baseband stage 40 attenuate and/orfilter out high-frequency components of the downconverted signal toproduce an output that includes the component of the selected inputsignal 90 that was transmitted within the selected channel. In theillustrated embodiment, baseband filters 42 each provide this output asa pair of differential output signals (96 a and 96 b) at output ports38. In particular embodiments, baseband filters 42 may be configured tohave a passband that is sized based on the minimum channel-spacing usedin the signals received at input ports 22. These tuned output signals 96may, in particular embodiments, represent a pair of quadrature,differential signals.

Because particular embodiments of tuner 10 may be designed for use inportable devices or other devices having space and power restrictions,the configuration and contents of baseband stage 40 may provide one ormore operational benefits in generating tuned output signals 96. As oneexample, the use of a folded cascode to couple mixers 32 a and 32 b tobaseband filters 42 a and 42 b, respectively, may allow tuner 10 tooperate with low headroom as described in greater below with respect toFIGS. 2A-2B. As another example, the contents and configuration offrequency generation circuit 60 may reduce interference between tuningsignals 86 and 88 generated by frequency generation circuit and othersignals traversing tuner 10, as described in greater detail below inFIG. 3.

FIGS. 2A and 2B illustrate a detailed view of particular portions ofbaseband stage 40 according to a particular embodiment. Shown in FIG. 2Aare example embodiments of mixer 32 a and baseband filter 42 that wereintroduced above with respect to FIG. 1. Additionally, FIG. 2A alsoillustrates a modulated current source 210, constant current sources 230and 232, and a folded cascode 220. Although FIG. 2A and the associatedtext describe, for the purposes of simplicity, only the portion ofbaseband stage 40 associated with mixer 32 a, the portion of basebandstage 40 that is associated with mixer 32 b may, with appropriatemodifications, use a similar configuration, as illustrated by FIG. 2B.

Modulated current source 210 receives preprocessed signal 92 from signalconverter 24 of RF stage 20 and modulates, based on the preprocessedsignal 92, a reference current that is produced by modulated currentsource 210. More specifically, in particular embodiments, modulatedcurrent source 210 outputs a modulated current signal 218 representingthe sum of the preprocessed signal 92 and the reference current. Inparticular embodiments, modulated current source 210 may receivepreprocessed signal 92 as a differential signal and may also outputmodulated current signal 218 as a differential signal pair (218 a and218 b) as shown in FIG. 2A.

Modulated current source 210, in the illustrated embodiment, includes apair of bipolar transistors (BJT) 212 and a pair of resistors 214 forreceiving the positive and the negative portion of the differentialpreprocessed signal 92. The emitter of each BJT 212 is coupled to groundthrough the corresponding resistor 214. Additionally, the base of eachBJT 212 is coupled to an appropriate biasing voltage 216. In general,however, modulated current source 210 may include any appropriatecomponents suitable to provide the described functionality. As oneexample, although the illustrated embodiments of modulated currentsource 210 includes BJT 212, modulated current source 210 may includeany appropriate form of transistors instead of or in addition to BJTs212.

Folded cascode 220 provides a low-impedance path for downconvertedsignal 94 between mixer 32 a and baseband filter 42 a. In theillustrated embodiment, folded cascode 220 is configured to receivedownconverted signal 94 as a differential signal pair (94 a and 94 b)applied to the source of two field-effect transistors (FETs) (222 a and222 b, respectively). FETs 222 are each biased by an appropriate biasingvoltage 224. In general, however, folded cascode 220 may represent anyappropriately configured cascode 220 coupling mixer 32 a and basebandfilter 42 a.

Constant current sources 230 and 232 supply a fixed output current. Morespecifically, in the illustrated embodiment, constant current sources230 and 232 are each capable of producing a constant differentialcurrent-mode signal. In general, however, constant current sources 230and 232 may each include any appropriate components suitable to providethe described functionality, and may include identical or differingcomponents.

In operation, baseband stage 40 receives preprocessed signal 92 acrossnodes 290 a and 290 b. Baseband stage 40 uses the received preprocessedsignal 92 to modulate the output of modulated current source 210. As aresult, modulated current source 210 outputs a modulated current signal218 that includes information from preprocessed signal 92. In particularembodiments, modulated current signal 218 represents a sum ofpreprocessed signal 92 and a reference current signal generated bymodulated current source 210. Modulated current signal 218 istransmitted to mixer 32 a.

Based on a tuning signal 86 received from frequency generation circuit60, mixer 32 a downconverts a portion of modulated current signal 218that is associated with a selected channel. Particular embodiments ofmixer 32 may utilize a tuning signal 86 that is generated as describedbelow with respect to FIG. 3. Mixer 32 then outputs the downconvertedinformation as downconverted signals 94 a and 94 b, a differentialsignal pair. As a result, information that was transmitted in theselected channel is output as a baseband component of downconvertedsignals 94.

At nodes 290 c and 290 d, downconverted signals 94 are routed towardsfolded cascode 220 as a result of the relatively higher input impedanceof constant current source 230 by comparison to that of folded cascode220. Downconverted signal 94 is then routed through folded cascode 220to nodes 290 e and 290 f. At nodes 290 e and 290 f, downconvertedsignals 94 are routed into baseband filter 42 a as a result of therelatively higher input impedance of constant current source 232 bycomparison to baseband filter 42 a.

Baseband filter 42 a filters downconverted signals 94, attenuating aportion of the downconverted signals 94 that is outside a particularpassband associated with baseband filter 42 a. Baseband filter 42 aoutputs the filtered downconverted signals 94 as output signals 96,which may also represent a differential signal pair. In particularembodiments, baseband filter 42 a may induce a gain in downconvertedsignal 94 that is reflected in output signal 96. Additionally, inparticular embodiments, baseband filter 42 a may convert downconvertedsignals 94 from current-mode signals to voltage-mode signals.

As a result of the folded cascode 220 conveying downconverted signal 94from the output of mixer 32 and into the input of baseband filter 42 a,baseband stage 40 may be able to operate with reduced headroom. Morespecifically, the low-impedance output path provided by folded cascode220 allows particular embodiments of tuner 10 to operate with only 2.5 Vheadroom. Moreover, as a result of this low headroom requirement,particular embodiments of tuner 10 may draw less power while operatingand be capable of operating with a lower-voltage battery. Additionally,because of the use of modulated current source 210 to feed the signalreceived by baseband stage 40 into mixer 32 a, baseband stage 40 mayelectronically isolate tuning signal 86 from preprocessed signal 92,resulting in better overall noise figures for tuner 10. Thus, certainembodiments of baseband stage 40 may provide multiple operationalbenefits. However, particular embodiments may provide some, none, or allof these benefits.

FIG. 3 illustrates the configuration and operation of particularembodiments of frequency generation circuit 60. As noted above,frequency generation circuit 60 generates tuning signal 86 andphase-shifted tuning signal 88, which are used by mixers 32 indownconverting preprocessed signal 92. Although FIG. 1 illustrates anembodiment of frequency generation circuit 60 in use with a particularembodiment of tuner 10, frequency generation circuit 60 may be usedindependently of the tuner 10 shown in FIG. 1. The illustratedembodiment of frequency generation circuit 60 generates signals for useby mixers 32 and transmits these signals to mixers 32 along a frequencygeneration path 410. In particular embodiments, frequency generationpath 410 couples an oscillator 420, a frequency divider 430, andquadrature generator 440.

Oscillator 420 generates oscillator signal 450, a periodic signalgenerated at a particular frequency that is determined based on thefrequency of the signal to be downconverted by mixers 32. In theillustrated embodiment, oscillator 420 generates oscillator signal 450as a differential signal pair (450 a and 450 b). Oscillator 420 maycomprise all or a portion of a frequency synthesizer using aphase-locked loop (PLL). In particular embodiments, oscillator 420 maybe capable of producing tuning signals in a frequency range much higherthan that of the input signals 90 received by tuner 10.

Frequency divider 430 divides the frequency of oscillator signal 450 bysome factor (referred to here as a “divisor”) resulting in a dividedoscillator signal 452. For example, in particular embodiments, frequencydivider 430 may be capable of dividing the frequency of oscillatorsignal 450 by a divisor equal to any multiple of two from two to N (forexample, in particular embodiments, N equals 32). As a result of thisflexibility, such embodiments of tuner 10 may be capable of tuningchannels received in several different bands of the radio-frequencyspectrum. In general, however, frequency divider 430 may include anyappropriate combination of components suitable to divide the frequencyof oscillator signal 450 by any appropriate divisor or divisors.

In the illustrated embodiment, frequency divider 430 includes aplurality of divider cells 432 and a plurality of switches 434. Dividercells 432 each divide the frequency of the signal received by thatdivider cell 432. Switches 434 are each capable of switching one or moredivider cells 432 into frequency generation path 410. Because eachdivider cell 432 may be configured to divide the frequency of the signalreceived by that divider cell 432 by a particular divisor, the finalfrequency of the signal received by quadrature generator 440 may beadjusted by switching divider cells 432 in and out of frequencygeneration path 410.

Quadrature generator 440 receives divided oscillator signal 452 fromfrequency divider 430 and induces a ninety-degree (90°) phase shift inthe received signal. Quadrature generator 440 then outputs a copy of thereceived divided oscillator signal 452 as tuning signal 86 (as shown inFIG. 1) and the phase-shifted copy of divided oscillator signal 452 asphase-shifted tuning signal 88 (as also shown in FIG. 1). Quadraturegenerator 440 may include any appropriate collection of componentssuitable to induce a phase shift in divided tuning signal 450.

In addition to frequency generation circuit 60, FIG. 3 also shows aplurality of conductive paths 460 that carry signals across all orportions of tuner 10. For the purposes of this description and theclaims that follow, “conductive path” may represent any path capable ofpropagating an input signal 90, preprocessed signal 92, downconvertedsignal 94, output signal 96, reference signal, biasing signal, supplyvoltage, and/or any other appropriate voltage or current back to aninput of mixing stage 30. In particular embodiments, conductive paths460 may include some or all of input paths 100, shown in FIG. 1.Furthermore, in particular embodiments, due to the layout of tuner 10and the location of particular elements of tuner 10, frequencygeneration path 410 crosses one or more conductive paths 460 and/or thephysical path traced by frequency generation path 410 comes sufficientlyclose to conductive paths 460 for the oscillator signal 450 to coupleinto signals that are propagating on conductive paths 460 at the same orapproximately the same frequencies. Thus, as described further below, inparticular embodiments, the elements of frequency generation circuit 60may be positioned so as to reduce and/or eliminate such interference.

In operation, oscillator 420 generates oscillator signal 450 andtransmits oscillator signal 450 down frequency generation path 410. Inparticular embodiments, the frequency of oscillator signal 450 is set bya user or another component coupled to tuner 10 and communicated tooscillator 420 through a programmable interface (not shown). Moreover,the frequency communicated to oscillator 420 may be selected by the useror the appropriate component based on a selected frequency associatedwith a particular channel of information in input signal 90 that tuner10 is being requested to tune. In particular embodiments, the frequencyof oscillator signal 450 generated by oscillator 420 is a multiple ofthe selected frequency.

As oscillator signal 450 traverses frequency generation path 410,oscillator signal 450 may cross one or more conductive paths 460 and/orpropagate sufficiently close to one or more conductive paths 460. Forexample, in the illustrated embodiment, frequency generation path 410crosses conductive paths 460 at least at point 490. Signals propagatingon conductive paths 460 couple into signals traversing frequencygeneration path if the signals traversing frequency generation path 410are propagating at the same or approximately the same frequency as thesignals traversing conductive paths 460. To avoid this problem and/or toreduce its effect, particular embodiments of frequency generationcircuit 60, may utilize an embodiment of oscillator 420 that generatesan oscillator signal 450 having a frequency substantially greater thaninput signals 90 and other signals that propagate across tuner 10. As aresult, this may reduce and/or prevent interference between oscillatorsignal 450 and other signals propagating across tuner 10.

Frequency divider 430 receives oscillator signal 450 and, depending onthe selected frequency, may divide oscillator signal 450 to produce atuning signal 86 having a frequency the same or approximately the sameas the selected frequency. In the illustrated embodiment, frequencygeneration circuit 60 may select one or more switches 434 to switch sothat a particular number of divider cells 432 are included in frequencygeneration path 410. Frequency divider 430 outputs divided oscillatorsignal 452 to quadrature generator 440. Depending on the number ofdivider cells 432 switched into the frequency generation path 410,frequency divider 430 outputs a divided oscillator signal 452 with afrequency equal to the frequency of oscillator signal 450 divided bysome divisor. For example, in particular embodiments, divider cells 432may each be configured to divide by two the frequency of the signalreceived by the divider cell 432. As a result, frequency divider 430 maydivide the frequency of oscillator signal 450 by some multiple of twothat is determined by the number of divider cells 432 that frequencydivider 430 has switched into frequency generation path 410.

Quadrature generator 440 receives divided oscillator signal 452 fromfrequency divider 430. Quadrature generator 440 time shifts a copy ofdivided oscillator signal 452. Quadrature generator 440 then outputsdivided oscillator signal 452 as tuning signal 86 and the time-shiftedcopy of divided oscillator signal 452 as phase-shifted tuning signal 88.Mixer 30 uses tuning signal 86 and phase-shifted tuning signal 88 todownconvert preprocessed signal 92 and output downconverted signals 94as described above with respect to FIGS. 1 and 2A-2B.

Thus, in particular embodiments of frequency generation circuit,frequency divider and/or divider cells 432 are located on frequencygeneration path 410 in a manner such that, wherever frequency generationpath 410 is sufficiently close to conductive paths 460 to induce noisein oscillator signal, oscillator signal 450 propagates at a higherfrequency than input signals 90, preprocessed signals 92, downconvertedsignals 94, output signals 96, and/or other appropriate signalstraversing conductive paths 460. Consequently, frequency generationcircuit 60 may reduce and/or eliminate the noise oscillator signal 450induces in particular frequency components of the signals propagating onconductive paths 460. Thus, particular embodiments of tuner 10 mayinclude embodiments of frequency generation circuit 60 that providemultiple advantages. Particular embodiments of tuner 10, however, mayprovide some, none, or all of these advantages.

Although the present invention has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the scope of the appended claims.

1. A system for tuning a radio-frequency signal, comprising: a firstinput path operable to propagate a first single-ended input signal to aselector; a second input path operable to propagate a secondsingle-ended input signal to the selector; a common reference generatoroperable to generate a reference signal; a selector operable to: convertthe first single-ended input signal to a first differential input signalusing the common reference signal; convert the second single-ended inputsignal to a second differential input signal using the common referencesignal; selectively couple one of the first input path and the secondinput path to an input of a mixer; the mixer operable to: receive aselected one of the first differential input signal and the seconddifferential input signal from the selector; downconvert at least aportion of the selected input signal; and output the downconverted inputsignal; the filter operable to: receive the downconverted input signal;attenuate a portion of the downconverted input signal that is outside apassband associated with the filter; and output at least a portion ofthe downconverted signal that is within the passband associated with thefilter.
 2. The system of claim 1, wherein the selector is furtheroperable to: convert the first single-ended input signal from avoltage-mode signal to a current-mode signal; and convert the secondsingle-ended input signal from a voltage-mode signal to a current-modesignal.
 3. The system of claim 1, wherein: the first single-ended inputsignal is associated with a first portion of a radio-frequency spectrum;the second single-ended input signal is associated with a second portionof the radio-frequency spectrum; and the first portion of theradio-frequency spectrum is greater than the second portion of theradio-frequency spectrum.
 4. The system of claim 3, wherein the firstportion of the radio-frequency spectrum comprises at least a portion ofthe very high frequency (VHF) spectrum.
 5. The system of claim 3,wherein the first portion of the radio-frequency spectrum comprises atleast a portion of the ultra high frequency (UHF) spectrum.
 6. Thesystem of claim 3, wherein the second portion of the radio-frequencyspectrum comprises at least a portion of the L-band.
 7. The system ofclaim 1, wherein: the mixer comprises a first mixer; the filtercomprises a first filter; and further comprising: a second mixeroperable to: receive the selected differential input signal from theselector; shift a phase associated with the selected differential inputsignal; downconvert at least a portion of the phase-shifted inputsignal; and output the downconverted phase-shifted input signal; thesecond filter operable to: receive the downconverted phase-shifted inputsignal from the second mixer; attenuate a portion of the downconvertedphase-shifted input signal that is outside a passband associated withthe second filter; and output at least a portion of the downconvertedphase-shifted input signal that is within the passband associated withthe second filter.
 8. A system for receiving radio-frequency signalscomprising: a conductive path operable to couple at least one of avoltage and a current to an input of a mixer, wherein the at least oneof the voltage and the current is associated with one or morefrequencies within a first range of frequencies; an oscillator operableto generate an oscillator signal wherein the oscillator signal isassociated with a frequency within a second range of frequencies; atuning path operable to couple the oscillator signal to a tuning inputof the mixer, wherein the tuning path crosses the conductive path atleast at a first point; a frequency divider located on the tuning pathbetween the first point and the tuning input of the mixer and operableto generate a divided oscillator signal based on the oscillator signal,and wherein the divided oscillator signal is associated with a frequencywithin the first range of frequencies; and the mixer operable to:receive, at the signal input of the mixer, the input signal from theconductive path; receive, at the tuning input of the mixer, the dividedoscillator signal from the tuning path; downconvert the input signalbased on the divided oscillator signal; and output at least a portion ofthe downconverted input signal.
 9. The system of claim 8, wherein thefrequency divider comprises: a switch operable to switch a divider cellinto the tuning path; and the divider cell operable, when switched intothe tuning path, to generate the divided oscillator signal by dividingthe frequency associated with the oscillator signal.
 10. The system ofclaim 8, wherein the frequency divider is associated with a set ofdivisors and operable to divide the frequency associated with theoscillator signal by any of the divisors in the set of divisors.
 11. Thesystem of claim 10, wherein the frequency divider comprises: a pluralityof switches, each switch operable to switch one or more of a pluralityof divider cells into the tuning path; and the plurality of dividercells, and wherein the frequency divider is operable to divide thefrequency of the oscillator signal by one of the divisors in the set ofdivisors by switching a number of divider cells associated with thatdivisor into the tuning path.
 12. The system of claim 8, wherein themixer comprises a first mixer; and further comprising: a quadraturegenerator operable to generate a phase-shifted oscillator signal byshifting a phase associated with a copy of the divided oscillatorsignal; and a second mixer operable to: receive the input signal; shifta phase associated with the input signal; downconvert at least a portionof the phase-shifted input signal, based on the phase-shifted oscillatorsignal; and output the downconverted phase-shifted oscillator signal.13. A method for tuning a radio-frequency signal, comprising: receiving,at a first input, a first single-ended input signal, wherein the firstinput is coupled to a selector by a first input path; receiving, at asecond input, a second single-ended input signal, wherein the secondinput is coupled to the selector by a second input path; generating, ata common reference generator, a reference signal converting the firstsingle-ended input signal to a first differential input signal using thereference signal; converting the second single-ended input signal to asecond differential input signal using the reference signal; coupling aselected one of the first input path and the second input path to aninput of a mixer; downconverting at least a portion of a selected one ofthe first differential input signal and the second differential inputsignal; attenuating a portion of the downconverted input signal that isoutside a passband associated with the filter; and outputting at least aportion of the downconverted input signal that is within the passbandassociated with the filter.
 14. The method of claim 13, furthercomprising: converting the first single-ended input signal from avoltage-mode signal to a current-mode signal; and converting the secondsingle-ended input signal from a voltage-mode signal to a current-modesignal.
 15. The method of claim 13, wherein: receiving the firstsingle-ended input signal comprises receiving a first input signalassociated with a first portion of a radio-frequency spectrum; andreceiving the second single-ended input signal comprises receiving asecond input signal associated with a second portion of theradio-frequency spectrum.
 16. The method of claim 15, wherein the firstportion of the radio-frequency spectrum comprises at least a portion ofthe very high frequency (VHF) spectrum.
 17. The method of claim 15,wherein the first portion of the radio-frequency spectrum comprises atleast a portion of the ultra high frequency (UHF) spectrum.
 18. Themethod of claim 15, wherein the second portion of the radio-frequencyspectrum comprises at least a portion of the L-band.
 19. The method ofclaim 13, wherein: the mixer comprises a first mixer; the filtercomprises a first filter; and coupling the selected one of the firstinput path and the second input path to the input of the mixer comprisescoupling the selected input path to the input of the first mixer and aninput of a second mixer; and further comprising: shifting a phaseassociated with the selected one of the first differential input signaland the second differential input signal; downconverting at least aportion of the phase-shifted input signal; attenuating a portion of thedownconverted phase-shifted input signal that is outside a passbandassociated with the second filter; and outputting at least a portion ofthe downconverted phase-shifted input signal that is within the passbandassociated with the second filter.
 20. A system for tuning aradio-frequency signal, comprising: means for receiving a firstsingle-ended input signal, wherein the first input is coupled to aselector by a first input path; means for receiving a secondsingle-ended input signal, wherein the second input is coupled to theselector by a second input path; means for generating a reference signalmeans for converting the first single-ended input signal to a firstdifferential input signal using the reference signal; means forconverting the second single-ended input signal to a second differentialinput signal using the reference signal; means for coupling a selectedone of the first input path and the second input path to an input of amixer; means for downconverting at least a portion of a selected one ofthe first differential input signal and the second differential inputsignal; means for attenuating a portion of the downconverted inputsignal that is outside a passband associated with the filter; and meansfor outputting at least a portion of the downconverted input signal thatis within the passband associated with the filter.
 21. The system ofclaim 20, further comprising: means for converting the firstsingle-ended input signal from a voltage-mode signal to a current-modesignal; and means for converting the second single-ended input signalfrom a voltage-mode signal to a current-mode signal.
 22. The system ofclaim 20, wherein: the means for receiving the first single-ended inputsignal comprises means for receiving a first input signal associatedwith a first portion of a radio-frequency spectrum; and the means forreceiving the second single-ended input signal comprises means forreceiving a second input signal associated with a second portion of theradio-frequency spectrum.
 23. The system of claim 22, wherein the firstportion of the radio-frequency spectrum comprises at least a portion ofthe very high frequency (VHF) spectrum.
 24. The system of claim 22,wherein the first portion of the radio-frequency spectrum comprises atleast a portion of the ultra high frequency (UHF) spectrum.
 25. Thesystem of claim 22, wherein the second portion of the radio-frequencyspectrum comprises at least a portion of the L-band.
 26. The system ofclaim 20, wherein: the mixer comprises a first mixer; the filtercomprises a first filter; and the means for coupling the selected one ofthe first input path and the second input path to the input of the mixercomprises means for coupling the selected input path to the input of thefirst mixer and an input of a second mixer; and further comprising:means for shifting a phase associated with the selected one of the firstdifferential input signal and the second differential input signal;means for downconverting at least a portion of the phase-shifted inputsignal; means for attenuating a portion of the downconvertedphase-shifted input signal that is outside a passband associated withthe second filter; and means for outputting at least a portion of thedownconverted phase-shifted input signal that is within the passbandassociated with the second filter.